Hi @onthebeach,
I am researching for a long lasting roofing materiel, we had a debate on this matter, I come up with Aluminum roofing materials, but those guys told me that TPO roofs are better than conventional metallic roofing.

GI roofing depends a lot on the climate, I gave a galvo roof at Hill End its first coat of paint in 1962 when it had been in place for 90 years; it's been repainted since and is still in very good order.

It's now 144 years old and there is no reason that it should not be there for 200 years or more.

Then you are one of the luckiest person on earth, here in this acidic urban climate GI sheets will not last long, Even GI water pipes cant afford the climate.